Virtually all microbial species have at least one antigen that is unique. These antigens can be purified and used to generate specific monoclonal antibodies. Both the antibodies and the purified antigens themselves provide effective and highly specific diagnostic tools.
The enzyme-linked immunosorbent assay (ELISA) is a common serological test for the presence of particular antigens or antibodies. There are two forms of this assay: (1) the direct ELISA employs monoclonal antibodies to detect the presence of a particular antigen in a sample; (2) the indirect ELISA is used to determine the presence of a specific antibody (e.g., HIV antibodies) in a specimen such as serum.

To see how the two ELISA tests are performed, click on the one of the options below.

The Direct ELISA

The Indirect ELISA